In recent years, with the development of an information and communication technologies, various wireless communication technologies have been developed. Among them, a wireless local area network (WLAN) is a technology that can wirelessly access the Internet in a home or a company or a specific service providing region by using portable terminals such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), and the like based on a wireless frequency technology.
In order to overcome a limit for a communication speed noted as a weak point in the WLAN, IEEE 802.11n has been provided as a technological standard established comparatively recently. IEEE 802.11n aims at increasing the speed and reliability of a network and extending a managing distance of a wireless network. In more detail, IEEE 802.11n supports high throughput (HT) in which a data processing speed is equal to or higher than maximum 540 Mbps, and is based on a multiple inputs and multiple outputs (MIMO) technology using multiple antennas at both a transmitter and a receiver in order to minimize a transmission error and optimize a data speed.
In a WLAN system, an active mode and a power save mode are supported as a management mode of a station (STA). The active mode means the operating mode in which the STA operates in an awake state to transmit/receive a frame. On the contrary, operation of the power save mode is supported for power saving of the STA which need not be in an activation state in order to receive the frame. The station (STA) that supports PSM operates in a doze state not in the case where the station can access a wireless medium to prevent unnecessary power consumption. That is, the STA operates in an awake state only during a period when the frame can be transmitted to the corresponding STA or during a period when the corresponding STA can transmit the frame.
In the WLAN system, an access point (AP) manages traffic to be transmitted to the STAs that operate in the power save mode. When there is provided buffered traffic to be transmitted to a specific STA, the AP requires a method to notify the buffered traffic to the corresponding STA and transmit the frame. Further, a method is required, in which when the STA operates in the doze state, the STA determines whether the buffered traffic to the STA itself exists and when the buffered traffic exits, the doze state of the STA is switched to the awake state, and the STA can normally receive the frame.